1. Field of the Invention
The present invention relates to a gain calculating device for calculating a white balance gain suitable for at least an image captured through strobe illuminated photography.
2. Related Art
In the field of cameras, there has been widely known a white balance technique for correcting the color of a captured image according to the type of a light source employed at the time of capture of the image, and the like. This technique is an image processing technique for eliminating a discrepancy between an impression which a photographer had during photographing action and an impression given by an output image, which is caused by the color of the light source employed during photography.
A technique for taking into consideration, during such white balance processing, whether or not strobe light has been fired during photographing action has hitherto been known. For instance, Japanese Patent Laid-Open Publication No. 2000-92509 describes calculation of a white balance gain by use of a strobe standard value previously set for strobe illuminated photography upon notification of tiring of a strobe light. According to this technique, a strobe standard value is always constant, regardless of the degree of contribution of strobe light to a subject. Therefore, when strobe light has not sufficiently reached the subject or when strobe light has been radiated with excessive intensity on the subject, there arises a problem of a failure to compute an appropriate white balance gain.
Accordingly, there has hitherto been practiced a technique of estimating, during strobe illuminated photography, the degree of contribution of strobe light, the degree of contribution of an ambient light source, the degree of contribution of strobe light, and the like; and adjusting a white balance gain according to the thus-estimated degrees of contribution and the like. For instance, Japanese Patent Laid-Open Publication No. Hei-4-326888 describes a technique for determining whether or not strobe light reaches a subject, on the basis of a distance to the subject. When the strobe light is determined not to be able to reach the subject, a preset value of a white balance is made selectable. Further. Japanese Patent Laid-Open Publication No. 2003-244467 describes a technique of detecting an area where a degree of mixing of ambient light and flash light is larger than a predetermined value, on the basis of information about ambient light existing during photographing action (the type of an ambient light source and the like), information about flash light employed (luring photographing action (presence/absence of flash light, the intensity of flash-reflected light, and the like), and the like. On the basis of a ratio of the detected area to the entire area, specifics of image processing, such as white balance processing, and the like, are determined. According to these conventional techniques, even when an image has been photographed by strobe light, the degree of mixing of strobe light (i.e., the degree of contribution of strobe light) is taken into consideration. Hence, a comparatively-appropriate white balance gain can be acquired.
However, any of these conventional techniques involves estimating the degree of contribution of strobe light from information extracted from factors other than a captured image such as a distance to a subject and information about flash light. Therefore, the conventional techniques cannot be said to have a high degree of precision in estimating the degree of contribution of strobe light. The low degree of precision in estimating the degree of contribution of strobe light poses difficulty in performing white balance processing suitable for strobe illuminated photography.